López, M., A. de Castro, J. Gutiérrez, and E. Leidi. “Nitrate and Potassium Concentrations in Cotton Petiole Extracts As Influenced by Nitrogen Fertilization, Sampling Date and Cultivar”. Spanish Journal of Agricultural Research, Vol. 8, no. 1, Mar. 2010, pp. 202-9, doi:10.5424/sjar/2010081-1159.